Chimney vents
Gases and fumes rising up the chimney are expelled outside by Chimney Vents. The “Venturi Effect” that takes place inside prevents downdraft. What's more, they're really easy to install which is down to being self-centring and calibrated. They have a drip edge on the base as well as on the crown to protect the chimneys from the rain. They're designed to keep water out when it rains.